netdev - Re: Problem: BUG_ON hit in ppp_pernet() when re-connect after changing shared key on LAC

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Message-ID: <CAM_iQpVyNghNJHES5-npZgYGFXps0-XTwJyJ-9pLDAuYJ_syWw@mail.gmail.com>
Date:	Tue, 5 Jul 2016 10:59:55 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Matt Bennett <Matt.Bennett@...iedtelesis.co.nz>
Cc:	"linux-ppp@...r.kernel.org" <linux-ppp@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"g.nault@...halink.fr" <g.nault@...halink.fr>
Subject: Re: Problem: BUG_ON hit in ppp_pernet() when re-connect after
 changing shared key on LAC

On Mon, Jul 4, 2016 at 7:50 PM, Matt Bennett
<Matt.Bennett@...iedtelesis.co.nz> wrote:
> Using printk I have confirmed that ppp_pernet() is called from
> ppp_connect_channel() when the BUG occurs (i.e. pch->chan_net is NULL).
>
> This behavior appears to have been introduced in commit 1f461dc ("ppp:
> take reference on channels netns").

We have some race condition here, where a parallel ppp_unregister_channel()
could happen while we are in ppp_connect_channel().

We need some synchronization for them. I am not sure what is the right lock
here since ppp locking looks crazy.